I. Field of the Invention
The present invention relates to internal combustion engines having a cold start fuel system and, more particularly, to a system for dissipating fuel in the cold start fuel passageway during engine shut down or start up.
II. Description of Related Art
Governmental regulations restrict the maximum amount of hydrocarbon, nitrous and other emissions from an internal combustion engine of the type using liquid fuel in automotive applications. A critical factor, however, affecting the hydrocarbon emissions from an internal combustion engine occurs during the xe2x80x9ccold startxe2x80x9d phase immediately following ignition of the engine from a cold ambient condition.
During the cold start phase for the automotive engine, which typically lasts for approximately two minutes following engine ignition, the catalytic converter of the type used in automotive vehicles is cold and thus ineffective in reducing automotive emissions from the exhaust stream. Additionally, fuel enrichment is oftentimes necessary to ensure satisfactory engine ignition when the engine is in a cold state.
Consequently, during a cold start of the automotive internal combustion engine, the air/fuel ratio is much richer than stoichiometric combustion, typically 10-14:1. However, up to 50% of the hydrocarbon emissions permitted by government regulations can occur during the first twenty seconds or so following engine ignition. Furthermore, these governmental emission restrictions become increasingly stringent with the passage of time.
In order to reduce hydrocarbon emissions during cold start of the invention, it is desirable to start the engine with a stoichiometric or lean fuel charge, i.e. an air/fuel ratio in the range of 14.5-16.1. In order to achieve such a lean fuel mixture during an engine cold start and still ensure satisfactory ignition of a cold engine, there have been a number of previously known cold start fuel systems which provide the fuel charge to the combustion chambers of the engine during a cold engine start condition in lieu of the multipoint fuel injectors which normally provide fuel to the engine during a warm engine condition. One such cold start fuel system is disclosed in U.S. Pat. No. 5,894,832, entitled xe2x80x9cCold Start Engine Control Apparatus and Methodxe2x80x9d and which issued on Apr. 10, 1999.
These previously known cold start fuel systems typically comprise a cold start fuel passageway having one end fluidly connected through a valve to the intake manifold of the engine upstream from the throttle. The second or downstream end of the cold start fuel injector is fluidly open to the intake manifold, typically immediately adjacent the engine combustion cylinders. A cold start fuel injector under control of the fuel management system for the engine controls actuation of the cold start fuel injector to inject fuel into the cold start fuel passageway. One or more heaters are then typically contained within or adjacent the cold start fuel passageway to enhance vaporization of the fuel prior to its introduction to the engine combustion chambers.
These previously known cold start fuel injector systems have proven satisfactory in use as well as compliant with government emission regulations as long as the engine, following engine emission, proceeds from a cold engine ignition and to a warm engine operating condition at which the cold start fuel injector is deactivated and fuel is instead provided to the engine through the conventional multipoint fuel injectors. Conversely, several problems arise where the engine, following engine ignition, is shut down prior to a warm engine operating condition. When this occurs, i.e. when engine shut down occurs while the cold start fuel injector is still supplying the engine with its fuel vapor charge, fuel vapors can and do remain in the cold start fuel passageway. Indeed, in some cases, pooling of liquid fuel can occur in the cold start fuel passageway when an engine shut down occurs during the cold start operation of the engine.
Still other engine conditions and/or malfunctions can also result in fuel vapor or pooled fuel in the cold start fuel passageway. For example, a malfunctioning cold start heater or cold start fuel injector can also result in fuel vapor or pooled fuel in the cold start passageway.
The presence of fuel vapor or liquid fuel within the cold start fuel passageway disadvantageously can increase the emission of hydrocarbon and other noxious emissions during the next subsequent engine start up. Furthermore, if excessive fuel vapor remains in the cold start fuel passageway upon the subsequent engine start up, undesirable backfiring of the engine can even occur.
There are no previously known systems or procedures for dissipating fuel vapors and fuel contained within the cold start passageway in the event of a premature engine shut down, i.e. shut down of the engine during a cold operating condition, or other engine conditions or component malfunctions.
The present invention provides both a system and procedures for dissipating fuel and fuel vapors contained within the cold start passageway of a cold start fuel system for an internal combustion engine.
In brief, the method and system of the present invention is designed for use with an internal combustion engine of the type used in automotive vehicles. These automotive engines include a cold start fuel system having both a cold start fuel injector as well as a cold start fuel passageway. During a cold engine operating condition, the cold start fuel injector provides fuel to the engine in lieu of the multipoint fuel injectors used during a warm engine condition by injecting fuel into the cold start fuel passageway. A heater within the cold start fuel passageway vaporizes the fuel and this fuel vapor is then inducted into the internal combustion engine in the desired fashion.
The system of the present invention includes an engine control unit (ECU) which determines the probability of fuel within the cold start fuel passageway either at engine shut off or engine turn on. There are a number of different ways of determining the probability of fuel within the cold start fuel passageway. For example, an engine shut down during a cold start operating condition is indicative of fuel vapor within the cold start fuel passageway.
Similarly, the current through the heater of the cold start fuel heater can be stored upon engine shut off in digital memory accessible by the engine control circuit. Thereafter, upon a subsequent engine start up, the previously stored value of the heater current is examined by the engine control circuit to determine if that heater current value is above a predetermined threshold. If not, indicative of a heater malfunction, there is a probability of fuel or fuel vapors in the cold start passageway upon a subsequent use of the cold start system upon the next engine start up.
Similarly, the duty cycle of activation of the cold start fuel injector can also be determined and compared with an acceptable range. If this duty cycle is outside the acceptable range, it is indicative of a malfunction of the cold start injector. Operation of the cold start system upon the next engine start up could result in fuel or fuel vapor within the cold start fuel passageway.
In the event that the ECU determines the probability of fuel within the cold start fuel passageway, the present invention provides a number of different procedures programmed in the ECU designed to dissipate the fuel from the cold start fuel passageway. These procedures minimize the creation of noxious emissions and hydrocarbons and even prevent possible backfiring of the internal combustion engine.
In a first procedure, in the event that there is a probability of fuel within the cold start passageway, the engine control circuit maintains activation of the cold start heater by providing electrical power to the cold start heater for a predetermined period following the transition from the cold start engine operating condition and to a warm engine operating condition. The continued activation of the heater even after the cold start fuel injectors have been deactivated ensures that any fuel that may be present on the heater is dissipated and supplied to the engine.
In yet a different procedure, in the event that the engine is shut down during a cold start engine operating condition, the multipoint fuel injector system is activated for a predetermined period of time despite engine shut down to ensure a few revolutions of the engine. The continued revolution of the engine thus inducts any fuel vapors which may be present in the cold start fuel passageway into the engine for combustion.
In yet a further procedure to dissipate fuel vapors present within the cold start fuel passageway, the ECU delays the initiation of the spark ignition system for the engine for a few revolutions upon a subsequent engine start up condition. Such delay in the initiation of the spark system ensures that fuel vapors contained within the cold start fuel passageway are inducted to the engine combustion chambers. Such delay in the initiation of the spark ignition system also reduces or completely eliminates the possibility of backfiring of the engine. Additionally, preferably the throttle is in a closed position while dissipating the vapors from the cold start fuel passageway so that the air inducted by the rotation of the engine passes through the cold start fuel passageway.